1. Field of the Invention
The present invention relates generally to an apparatus including a Transmission/Reception (TX/RX) antenna switch in a time division duplex (TDD) wireless communication system. More particularly, the present invention relates to an apparatus for protecting an RX low-noise amplifier (LNA) from a radio-frequency (RF) TX signal using a 180° hybrid coupler.
2. Description of the Related Art
In a TDD wireless communication system, the same frequency is time-divided for both a transmission signal and a reception signal. A TDD wireless communication system includes a TX/RX antenna switch (TRAS) unit that performs switching between a high-power RF TX signal and a low-power RF RX signal. In a TX mode, the TRAS unit protects an RX LNA by blocking TX power flowing into the RX LNA. In an RX mode, the TRAS unit prevents a decrease in RX sensitivity by reducing a noise received from the TX side.
FIG. 1 is a block diagram illustrating a conventional TDD wireless communication system using a TRAS unit.
Referring to FIG. 1, the conventional TDD wireless communication system includes a TDD controller 100, a transmitter 102, a power amplifier (PA) 104, a receiver 106, an LNA 108, a TRAS unit 110, a front-end unit 112 and an antenna 114.
The TDD controller 100 generates a control signal for controlling an operation of a TX/RX mode according to the time-division scheme and outputs the generated control signal to the transmitter 102, the receiver 106 and the TRAS unit 110.
The PA 104 amplifies a TX signal output from the transmitter 102 into a high-power TX signal and outputs the high-power TX signal to the TRAS unit 110. The LNA 108 amplifies an output signal of the TRAS unit 110 and outputs the resulting signal to the receiver 106.
In response to the control signal received from the TDD controller 100, the TRAS unit 110 switches between TX and RX paths to perform an operation of a TX/RX mode. That is, if the control signal received from the TDD controller 100 indicates a TX mode operation, the TRAS unit 110 connects (creates) a TX path from the PA 104 to the antenna 114 to output the high-power TX signal received from the transmitter 102 to the front-end unit 112 and to prevent the high-power TX signal from flowing into the LNA 108. If the received control signal indicates an RX mode operation, the TRAS unit 110 connects (creates) an RX path from the antenna 114 to the LNA 108 to output an RX signal received from the front-end unit 112 to the LNA 108 and to block a noise received from the PA 104.
Because an insertion loss of the TX path may affect the capacity of the PA in the TX mode, the TRAS unit 110 must be designed and configured in such a way to minimize the insertion loss of the TX path and to isolate the LNA from the TX path. Also, because an insertion loss of the RX path and a noise level of the input signal of the LNA may affect the RX performance in the RX mode, the TRAS unit must be designed and configured in such a way to minimize the insertion loss of the RX path and to isolate the output terminal of the PA from the RX path.
Conventionally, the TRAS unit 110 is implemented using an RF switch or circulator, thereby isolating the TX and RX paths to protect the LNA 108. However, if there is a failure in the power supply of the TRAS unit using the RF switch or circulator, the TX and RX paths cannot be isolated and the LNA cannot be protected.